From personal experience the ban of 2 days/perm is usually decided by the total level of the account not what skill was botted. Any account that I've ever had over 700+ total level has only ever been 2 dayed and not permed straight away, however I would guess this would change if you've had a shit load of 2 days on the same ip (use proxys to overcome that)
If you wanted to bot some thieving instead of doing 1 big four hour session just break it down into 30-60 min sessions with breaks that way you could do all your botting in 1/2 days
edit: not saying this is all definite just from my own experiences!